How player elimination should work?
As a board game designer, we generally want to remove the idea of player elimination because that generally mean casting out a player that will watch television or go home for the rest of the game. I think in a video game, that could be still applied especially in a multiplayer games where you might want everybody to stay in the game until the end. So here is a few suggestion to remove player elimination.
Exile: Romance of the 3 kingdom has this notion of exile which could work like this in elemental. When you lose your capital city or when your character gets captured, you are forced into an exile. All left over cities turns neutral and can therefore be captured by anybody. Exile allows you to move on the map and do things like heroes could do. But one of the thing you can do is try to overthrown an ennemy city and take control of it to start a new empire OR offer magic support to another player.
People would argue that this would make the game never end. Well here is a way to make sure it can end. When a player is in exile, it is considered eliminated. So if a game is won by aliminating all players, that player can still win if there are a few exiled played around which start a new empire. In order for a player ot get back into a game, he needs to build his wizard tower (or any other thing you want) this would require time and resources. It might force the player to control at least 2 or 3 cities in order to successfully build it. It also gives time to the winning player to disturb the construction of the tower unless other players are keeping him buzy.
Note that it also depends on the victory conditions ( I will make another thread about it), here I assume that you had to eliminate everybody.
Vassals: The "Viktory 2" board game, introduced the concept of vassal which removed the player elimination in an elegant way. When you capture a capital, the loosing player becomes the vassal of the winning player. The vassal control his empire as normal but he cannot attack the winning player. The only way to get free is if another player capture his capital and agree to free him instead of making him a vassal of his own.
If the victory conditions ask to control a certain amount of population, the vassal empire's population is added to the total of the winning player for victory conditions. Still, sometimes in "viktory 2", it created a situation where a player could do no effort to protect their cities in order not to help the winning player. To make sure the vassal listen to the desires of the winning players, there could be some way for the winning player to enforce his autority. For example, he could seize magical artifacts, destroy buildings in the vassal city, move military units of the vassal player, etc. The vassal would still want to keep his kingdom in shape so that if he get free, he would be able to stand by himself.